Table 1. Accuracy comparison of various approximation methods (one-dimensional case)

Method	MAE	MaxAE	R2
Kriging	8.5111	15.2408	0.3076
Co-kriging	6.7748	14.7731	0.3236
HK	6.7842	14.7854	0.3226
3LK	3.7310	8.1480	0.8116